Let the doer summarize itself — and edit a dotfile without ever corrupting it

The reframe

Layer 2 (a "✨ Summarize" button) first re-read each session's transcript with a separate claude -p. It worked but took 20–50s — a second model re-doing the work and, at the user's high effort setting, thinking for thousands of tokens. The founder's reframe killed the whole problem in one sentence: the session's own Claude already did the work and holds the context — have it emit the summary as a byproduct of its reply. No re-read, no second call. Free, instant, accurate.

The mechanism

Give the pane's Claude a tiny directive: at the end of each reply, append <dk-summary>{viz json}</dk-summary>. The app then pulls that block out of the terminal stream (a small cross-chunk-safe stripper), so the user never sees it, and renders it as that session's card. Validated end-to-end: prompted with the directive, Claude reliably appended a valid, accurate block.

The gotcha: a wrapper on PATH lost to the user's rc

The first injection plan — drop a DalkkakAI claude wrapper on the pane's PATH — silently didn't fire. The user's ~/.zshrc does export PATH="$HOME/.local/bin:$PATH", which prepends the dir with the real claude ahead of ours. PATH order: real binary wins.

Fix: a shell function, not a PATH shadow. claude() { command claude --append-system-prompt … }. Functions resolve before PATH, so the same rc that re-orders PATH can't beat a function defined in it. (command claude calls the real binary — no recursion.)

The careful part: editing a dotfile that must never break

Installing that function means writing to ~/.zshrc — the user's terminal config. Two guardrails fired, both correctly:

1. The auto-mode safety classifier blocked my direct shell edit as an unrequested profile change. Right call. The founder then explicitly approved — "do it for sure… it must never get tangled" — so the app performs it (the proper, consented path).
2. So the install is bulletproof by construction: append-only — it never reads the file to rewrite it, never parses it, only appends a marked block, so existing content cannot be corrupted, only added to. Plus a one-time backup to ~/.zshrc.dalkkak-bak, an idempotent marker (no double-add), and a DALKKAK_PANE_ID guard so it acts only inside DalkkakAI panes.

Verified: after install the existing ~/.zshrc is byte-identical (append-only proven), the backup exists, and claude is a function inside DalkkakAI panes but the untouched real binary everywhere else.

Lessons

• To intercept a command in an interactive shell, override it with a function (beats PATH); a PATH-shadow loses to the user's own rc.
• When you must touch a user's dotfile: append-only + backup + idempotent marker + scope guard. Never parse-and-rewrite — that's how you corrupt someone's shell.
• The best fix for "the summary is slow" wasn't a faster summarizer; it was not summarizing twice — let the doer do it. (The founder's call, not mine.)

Commit: fad4738 · decision: docs/DECISIONS.md ADR-003